The disclosure of U.S. Provisional Application No. 61/491,080, filed May 27, 2011, is hereby incorporated herein in its entirety by reference.
Many harvesting machines and mowers utilize reciprocating sickle cutters for severing plant material from the ground. A trend has been to increase the overall width of these machines to an extent such that two or more of the cutters are employed in end to end relation. The cutters are typically driven from opposite ends to effect the cutting action, by mechanical or fluid driven mechanisms, such as a crank, epicyclic, or wobble drive. The cutters typically comprise an elongate, end to end assembly of cutter knives, which are attached at one end to the drive, for longitudinal reciprocating movement relative to longitudinally spaced, stationary blades or guards.
The sickle bar, which may weight as much as 60 pounds or more, typically must accelerate and decelerate two times per cycle as a result of the reciprocal movement. A typical speed for the sickle bar is up to about 16 hertz or cycles per second. The back and forth motion at a high cycle per second generates high acceleration values and high deceleration values that in turn generate high forces on the structural components. These high back and forth forces can have at least two negative effects, vibration at the sickle drive system that may be transmitted to other components of the machine causing discomfort for the operator, and fatigue failure of the structural components themselves. Also, when a sickle knife has a long length, the connecting structure for supporting and driving the knife must be more robust and heavy.
One proposed solution to the vibration problem is a timing shaft that extends between the different sickle drives and keeps them in time to cancel the vibration. However, this is costly and typically involves gears and shafts or timed belts and doesn't integrate well with fluid driven systems. Another proposed solution is a common drive, as disclosed in Abrahamson U.S. Pat. No. 5,157,906, but this would also require a very long connecting element for long sickle knives. Still another proposed solution, which eliminates the need for lengthy connecting apparatus, utilizes a rack and pinion mechanism connecting the knives. Reference in this regard, Polk et al., U.S. Pat. No. 6,889,492 B1. However, a simpler solution is still sought.
What is sought is a timing apparatus for independently driven and adjacent sickle cutting knives of a plant cutting machine which overcomes the problems, negative effects, and disadvantages and costs referenced above.